Быстрее!!! Sin 4пи/13 + sin 8пи/13 + sin 12пи/13

Question

Быстрее!!!
Sin 4пи/13 + sin 8пи/13 + sin 12пи/13

Answer 1

(sin4π/13+sin12π/13)+sin8π/13=2sin8π/13*cos4π/13+sin8π/13=
=sin8π/13*(2cos4π/13+1)